(1) Field of the Invention
The invention relates to a method and apparatus for producing an adhesive tape by supplying and applying an adhesive on a base material, and an adhesive tape.
(2) Description of the Relates Art
Conventionally, an adhesive tape is produced by means of a direct system in which an adhesive is applied as an application solution by an application roller on an elongated base material such as paper, plastic film or the like, or by means of a reverse system. These means are made up of a pair of laminate rollers 40 and 50 on which base materials 90 and 100 are wound, and which are oppositely disposed to each other while facing with a liquid reservoir 80 opened to air, as shown in FIG. 1.
In the above means, when the applying speed is high or when the viscosity of the adhesive is high, in particular, a phenomenon markedly arises that an air cell B in the liquid reservoir 80 is rolled together (involved) with rotation of the upper laminate roller 40. As a measure for avoiding involvement of air cells, for example, the following measures are proposed. First, there is proposed and practiced a measure which separates a liquid reservoir into a front part and a rear part along the width direction of a base material by means of a surface of a base material whose distal end is wound on a lower laminate roller, or by an air cell scraping-off plate provided at a certain interval (see JP-A 2002-177859).
Secondly, there is proposed and practiced a measure in which a suction space is provided in a gap between the bottom of a liquid reservoir and a roller so as to reduce entering of air cells from the gap (see JP-A 2003-53228).
However, these conventional measures suffer from the following problems.
In fact, the first and second measures are effective in removing air cells residing in the bottom of the liquid reservoir and in preventing the air cells from rolled together by the roller. However, these is still a problem that occurrence of air cells in an adhesive is inevitable because air is rolled together from the liquid surface of the liquid reservoir that is open to air with rotation of the upper roller.
In the conventional measures, when an adhesive having a viscosity ranging from 0.1 to 100 Pa·s is used, in particular, it is difficult to remove air cells occurring in the adhesive due to air involved from the liquid surface side, from the side of the bottom of the liquid reservoir.
Therefore, when an air cell occurring in the adhesive due to rotation of a roller is such a large cell that has a diameter ranging from several hundreds micrometers to several millimeters, a through hole occurs in an adhesive layer of a formed adhesive tape, leading deterioration in appearance and quality.